<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>盒子居中</title>
    <link rel="stylesheet" href="css/reset.css">
    <style type="text/css">
        .top_bar{
            width: 100%;
            height: 40px;
            background-color: #333;
        }
        .container{
            width: 80%;
            height: 100%;
            background-color: #444;
            /* margin-left: auto;
            margin-right: auto; */
            margin: 0 auto;
        }
    </style>
</head>
<body>
    <div class="top_bar">
        <div class="container">
`           小米商城
        </div>
    </div>
</body>
</html>